Investment in Affiliates and Related-Party Transactions - Schedule of Related Party in the Consolidated Income Statement Components (Details) - USD ($) $ in Millions	3 Months Ended					6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2023	Sep. 30, 2023	Dec. 31, 2024		Dec. 31, 2023		Dec. 31, 2022
Related Party Amounts Consolidated Income Statements [Abstract]
Total Expense	$ 2,344	$ 2,365	$ 2,301	$ 2,233	$ 2,259	$ 4,492	$ 6,793	$ 9,295	[1]	$ 9,158	[1]	$ 8,899	[1]
Corporate Joint Venture | Conrail
Related Party Amounts Consolidated Income Statements [Abstract]
Rents, Fees and Services								142		132		130
Purchase Price Amortization and Other								4		4		4
Equity Earnings								(69)		(54)		(44)
Total Expense								77		82		90
Related Party | TTX
Related Party Amounts Consolidated Income Statements [Abstract]
Equity Earnings								(50)		(49)		(51)
Car Hire Rents								256		249		241
Total Expense								$ 206		$ 200		$ 190

[1] See Note 20, Revision of Prior Period Financial Statements